[dev.ssa] cmd/compile: improve error message for phi location mismatch

Change-Id: I402841743fcdc287631646039eb149f5cfdf886c
Reviewed-on: https://go-review.googlesource.com/13269
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 5c56b370bd24be545a138de9a52e94a6a8156f17..041e32171733afa027a0e77004ce224b20ad4ab1 100644 (file)
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -2111,8 +2111,8 @@ func genValue(v *ssa.Value) {
                f := v.Block.Func
                loc := f.RegAlloc[v.ID]
                for _, a := range v.Args {
-                       if f.RegAlloc[a.ID] != loc { // TODO: .Equal() instead?
-                               v.Fatalf("phi arg at different location than phi %v %v %v %v", v, loc, a, f.RegAlloc[a.ID])
+                       if aloc := f.RegAlloc[a.ID]; aloc != loc { // TODO: .Equal() instead?
+                               v.Fatalf("phi arg at different location than phi: %v @ %v, but arg %v @ %v\n%s\n", v, loc, a, aloc, v.Block.Func)
                        }
                }
        case ssa.OpConst8, ssa.OpConst16, ssa.OpConst32, ssa.OpConst64, ssa.OpConstString, ssa.OpConstNil, ssa.OpConstBool: